1. Field of the Invention
The present invention relates to a droplet discharging apparatus, an image forming apparatus, and a preliminary discharge method, and more particularly, to preliminary discharge technology for droplets discharged from a discharging head.
2. Description of the Related Art
In recent years, inkjet recording apparatuses (inkjet printers) serving as recording apparatuses that print/record images or the like taken by digital still camera have become widely distributed. Inkjet recording apparatuses have a plurality of recording elements (nozzles) in the head, the recording head is moved to scan the recording medium while ink droplets are discharged from the recording elements to the recording medium, the recording medium is conveyed by a single line when one line of image has been recorded on recording paper, and an image is formed on the recording paper by repeating these steps.
There are inkjet printers that use a short serial head and record images while causing the head to scan in the width direction of the recording medium, or those that use a line head in which recording elements are arrayed across the entire range of one side of the recording medium. In printers in which a line head is used, images can be recorded on the entire surface of the recording medium by scanning the recording medium in the direction orthogonal to the array direction of the recording elements. In printers in which a line head is used, a carriage or another conveyance system for moving the short head back and forth is unnecessary, and complex scanning control for the carriage movement and recording medium is not required. Also, the recording medium alone moves, so recording speed can be increased in comparison with printers in which a serial head is used.
In an inkjet printer, for a reason of some kind, discharge errors may arise in a portion of the plurality of recording elements, for instance, ink may fail to be discharged, or the amount of ink discharged (the dot size formed by the droplet deposited on the recording medium) or the direction of flight thereof (the deposited position of the droplet) may be defective, or the like. The presence of defective recording elements of these kinds may cause the quality of the recorded image to be degraded, and hence it requires countermeasures.
Conventionally, discharge errors in the recording elements are prevented by removing thickened ink that has formed in the vicinity of the discharge ports, by performing preliminary discharge (purging), such as a dummy discharge, liquid discharge, or the like, at periodic intervals. Moreover, a method is also known whereby, if a discharge error is detected, then maintenance of the recording elements is carried out by means of the aforementioned purging operation, or by printing a test pattern, or the like. In general, in a purging operation, ink is discharged onto a maintenance member, such as a cap, but ink can be discharged onto the conveyance belt instead.
However, in the method for purging onto a conveyance belt, it is necessary to clean the conveyance belt satisfactorily after purging. If a cleaning method based on wiping the conveyance belt in one direction is adopted, then a problem may arise in that the dirt cannot be removed sufficiently. If the conveyance belt is used without having been cleaned satisfactorily, then this may cause degradation of the print quality in the printing results, such as transfer onto the rear side of the paper, or the like.
Japanese Patent Application Publication No. 2000-272770 discloses a sheet conveyance apparatus and image forming apparatus including a mechanism whereby the preliminary discharge position can be set in a variable manner, in accordance with the position of the paper. However, in Japanese Patent Application Publication No. 2000-272770, there is no disclosure regarding maintenance operations, such as preliminary discharge, or the like.
Japanese Patent Application Publication No. 2000-127362 discloses an inkjet recording apparatus comprising a head and a plurality of cleaning members, the conveyance belt being cleaned on the downstream side of the head. However, in the inkjet recording apparatus described in Japanese Patent Application Publication No. 2000-127362, cleaning devices are provided in equal number to the recording heads, and therefore the recording head and the cleaning devices become large in size, and control of the cleaning device and conveyance device becomes complicated.
Japanese Patent Application Publication No. 2001-105628 discloses an image forming apparatus comprising an ink receptacle body which is attachable to and detachable from the conveyance belt, and preliminary discharge is carried out into the ink receptacle body. However, in the image forming apparatus described in Japanese Patent Application Publication No. 2001-105628, there is a large opening in the conveyance belt, and hence the suction force required in order to prevent lifting up of the paper cannot be obtained.
Japanese Patent Application Publication No; 2002-103598 discloses a printer comprising a restoring region for restoring the discharging function of the printer head, situated over a conveyance belt having an opening therein, and a restoring operation of the printer head is executed in the restoring region. However, the printer described in Japanese Patent Application Publication No. 2002-103598 has a holder for holding the ink receptacle body over the conveyance belt, and therefore it is necessary to withdraw the printer head.